Method and apparatus for diagnosing status of parts in real time in plasma processing equipment

ABSTRACT

Apparatus and methods for diagnosing status of a consumable part of a plasma reaction chamber, the consumable part including at least one conductive element embedded therein. The method includes the steps of: coupling the conductive element to a power supply so that a bias potential relative to the ground is applied to the conductive element; exposing the consumable part to plasma erosion until the conductive element draws a current from the plasma upon exposure of the conductive element to the plasma; measuring the current; and evaluating a degree of erosion of the consumable part due to the plasma based on the measured current.

BACKGROUND

Plasma has been used in many applications, such as semiconductorprocessing steps. A conventional plasma processing equipment generatesplasma having harsh thermal and/or chemical properties, which causeswear to numerous parts that are exposed thereto during the processingsteps. Due to the aggressive nature of the plasma, repeated contact withthe plasma may cause one or more of the parts to erode gradually and/orfail abruptly, degrading the performance of the equipment and causingthe process result to change over time.

As such, it is important to carefully monitor the states of these partsand change the parts at the appropriate time. If they are changed toosoon, the production cost is increased by throwing away the parts whichcould still be used further. If they are left too long before changing,damage may result to other parts of the equipment leading to additionalcost. For instance, eroding an edge ring in a semiconductor processingchamber beyond the safe limit may result in destroying an electrostaticchuck which is a far more costly part. The ideal case is to use the partto the maximum safe limit and no further.

The useful lifetime of each part may be estimated through statisticalanalysis of degradation and failure when placed in specificenvironments. However, it is always possible that the part may fail orneed to be replaced earlier than expected. Also, in practice, thelifetime of the part may depend on exactly how the equipment is run,which may not be known or closely monitored. Furthermore, it may benecessary to open the equipment to perform an inspection, which isdisruptive to production and leads to a certain down-time. Thus, itwould be desirable to provide an ability to detect events indicative ofthe end of useful lifetime, faults, or failure of the part during theoperation of the equipment and independent of application in anyspecific plasma process. It would be further desirable to provide anability to monitor the state of each part in real time and calling of analarm when the end of effective operational lifetime of the part isreached.

SUMMARY

According to one embodiment, a method of diagnosing status of aconsumable part of a plasma reaction chamber wherein the consumable partincludes at least one conductive element embedded therein, includes thesteps of: coupling the conductive element to a power supply so that abias potential relative to the ground is applied to the conductiveelement; exposing the consumable part to plasma thereby causing theconductive element to draw a current from the plasma upon exposure ofthe conductive element to the plasma; measuring the current; andevaluating a degree of erosion of the consumable part due to the plasmabased on the measured current.

According to another embodiment, a consumable part of a plasma reactionchamber wherein the consumable part is formed of dielectric material andincluding a surface to be exposed to plasma, includes: one or moreconductive elements embedded in the consumable part; a probe circuitcoupled to the conductive elements; and a power supply coupled to theprobe circuit and ground to apply a bias potential to the conductiveelements relative to the ground, wherein the conductive elements areoperative to draw a current from the plasma upon exposure of theconductive element to the plasma and the probe circuit is operative tomeasure the current.

According to yet another embodiment, a consumable part of a plasmareaction chamber wherein the consumable part is formed of conductivematerial and including a surface to be exposed to plasma, includes: oneor more conductive elements embedded in the consumable part andelectrically insulated from the consumable part by a dielectric layer; aprobe circuit coupled to the conductive elements; and a power supplycoupled to the probe circuit and ground thereby to apply a biaspotential to the conductive elements relative to the ground, wherein theconductive elements are operative to draw a current from the plasma uponexposure of the conductive element to the plasma and the probe circuitis operative to measure the current.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic cross sectional diagram of a plasma processingchamber having a diagnostic sensor in accordance with one embodiment.

FIG. 2 shows an exemplary plot of signal from the diagnostic sensor inFIG. 1 as a function of time.

FIGS. 3A-3B show schematic side and top cross sectional views of an edgering in accordance with another embodiment.

FIGS. 4A-4B show schematic cross sectional views of various embodimentsof an edge ring.

FIG. 5 shows a schematic cross sectional diagram of an exemplaryembodiment of an upper electrode of the type to be used in the plasmaprocessing chamber in FIG. 1.

FIG. 6 shows a schematic cross sectional diagram of the upper electrodein FIG. 5, taken along the line VI-VI.

FIGS. 7A-7C show schematic cross sectional diagrams of various exemplaryembodiments of an upper electrode of the type to be used in the plasmaprocessing chamber in FIG. 1.

DETAILED DESCRIPTION

Referring now to FIG. 1, there is shown a schematic cross sectionaldiagram of a plasma processing chamber 100 in accordance with oneembodiment. It is noted that the chamber 100 is an exemplary device thatgenerates plasma and includes a diagnostic sensor according to oneembodiment. Hereinafter, for brevity, the following discussion islimited to sensors for diagnosing components in the chamber 100.However, it should be apparent to those of ordinary skill that thesimilar sensor embodiments can be applied to other suitable plasmagenerating devices.

As depicted, the chamber includes a wall 117 for forming a space withinwhich various components for generating capacitively coupled plasma aredisposed. The chamber also includes an electrostatic chuck 106 forholding a substrate 112 in place during operation and an upper electrode102. The upper electrode 102 and chuck 106 form a pair of electrodescoupled to an RF power source (not shown in FIG. 1) and generate plasmaover the top surface of the substrate 112 when powered by the RF source.The chamber 100 also includes a ceramic ring 108, a coupling ring 110disposed between the ceramic ring and the chuck 106, and an edge ring114 disposed around the edge of substrate 112. The plasma is confined byconfinement rings 104 disposed in the gap between the upper electrode102 and chuck 106. Some of the gas particles in the plasma pass throughthe spacing/gaps between the rings 104 and thence are exhausted from thechamber by a vacuum pump.

The edge ring 114 performs several functions, including positioning thesubstrate 112 relative to the chuck 106 and shielding the underlyingcomponents not protected by the substrate itself from being damaged bythe plasma. The edge ring 114 also enhances plasma uniformity across thesubstrate 112. Without the edge ring 114, the substrate 112 electricallydefines the outer edge of the chuck and the equipotential lines wouldcurve upward sharply in the vicinity of the substrate edge. As such,without the edge ring 114, the substrate edge would experience adifferent plasma environment from the plasma environment that exists atthe center of the substrate, resulting in poor production yield near theedge. More detailed description of the chamber can be found in commonlyowned U.S. Pat. No. 6,986,765.

Due to the aggressive nature of the plasma, the edge ring 114 can wearaway over time. As the edge ring 114 wears away, the plasma propertiesin the vicinity of the damaged regions of the edge ring may change. Thechanges to the plasma properties in turn may cause the process result tochange over time and the chamber may reach a point where the edge ring114 needs to be replaced.

To monitor the operational condition and structural status of edge ring114 in real time and to provide an indication of an event, such as theend of useful lifetime of the edge ring, a diagnostic sensor 115 can becoupled to the edge ring 114. The sensor 115 includes a pickup unit orprobe 116 and a probe circuit 118 connected to the probe 116 via aconductor wire 119. The probe 116 is embedded in the edge ring 114 suchthat the probe is completely surrounded by the edge ring 114. In oneexemplary embodiment, the probe 116 has the shape of a wire segment orpin. The probe 116 is formed of, but not limited to, conductingmaterial, such as metal, while the edge ring 114 is formed of, but notlimited to, electrically insulating or dielectric material.

The probe circuit 118 includes a power supply 122 for applying anelectrical potential between the probe 116 and ground. The circuit 118also includes a resistor 120 and a measuring device 124, such asvoltmeter, for measuring the voltage across the resistor or theelectrical current flowing through the resistor. The conductor wire 119is shown to extend from the probe 116 through the chamber wall 117 tothe circuit 118. In an alternative embodiment, the circuit 118 may bedisposed inside the chamber and the measuring device 124 may be coupledto a display unit that is located outside the chamber wall 117 andoperative to display the signal measured by the device 124 to theoperator.

The probe 116 is embedded in the edge ring 114 at a depth correspondingto a diagnostic event, such as the end of useful lifetime of the edgering 114. The probe 116 is biased to a negative dc potential, preferablyof 10-15 volts, relative to the ground. During operation, the portion ofthe edge ring 114 covering the probe 116 from the plasma prevents theenergetic positive ions of the plasma from reaching the probe 116.However, upon repeated exposures to the plasma, the covering portion ofthe edge ring 114 may be eroded and expose the probe 116 to the plasma,causing the probe to draw an ion current from the plasma. The drawn ioncurrent flows through the resistor 120 of the probe circuit 118 and canbe measured by measuring the voltage across the resistor. The plasma canbe coupled to the ground via the wall 117, upper electrode 102, or othersuitable components and complete a path for the ion current drawn by theprobe, i.e., the plasma is a source of the ion current and forms a partof the electrical path for the ion current, wherein the ground alsoforms a part of the electrical path.

In an alternative embodiment, the probe 116 can be biased to a positivedc potential (not shown in FIG. 1), preferably of 10-15 volts, relativeto the ground. In this embodiment, the positive terminal of the powersupply 122 in FIG. 1 may be connected to the resistor 120 while thenegative terminal of the power supply 122 is connected to the ground.The positively biased probe 116 may draw a negative electron currentfrom the plasma when the edge ring 114 is worn out to expose the probe116 to the plasma. The plasma can be coupled to the ground via the wall117, upper electrode 102, or other suitable components and complete apath for the electron current drawn by the probe, i.e., the plasma is asource of the electron current and forms a part of the electrical pathfor the electron current, wherein the ground also forms a part of theelectrical path.

FIG. 2 shows an exemplary plot of signal from the measuring device 124in FIG. 1 as a function of plasma exposure time. As the portion of theedge ring 114 covering the probe 116 from the plasma is worn out, theion current flowing through the resistor 122, or, equivalently, thevoltage across the resistor measured by the device 124 may suddenlyincrease, as depicted in FIG. 2. This sudden increase in signalintensity may be used as an indicator of the point when the probe 116 isexposed to the plasma. In one embodiment, a warning or notificationrequiring operator attention or intervention may be triggered when thevoltage increases to a preset threshold voltage V_(T) that correspondsto a diagnostic event, such as the end of effective operational lifetimeof the edge ring 114. In another embodiment, warning or notification maybe triggered when the voltage shows a sudden change in value. Thus, bymonitoring the signal from the measuring device 124, an in situdiagnosis of condition, such as degree of erosion, and performance ofthe edge ring 114 can be performed in real time.

As discussed above, the probe 116 may be biased to a positive dcpotential relative to the ground and draw negative electron currents. Insuch a case, the vertical axis of the plot in FIG. 2 may represent theabsolute value of the voltage across the resistor 120.

In one exemplary embodiment, the sensor 115 may include multiple probepins embedded in the edge ring 114 in order to provide redundancy or tomonitor the overall integrity of the edge ring. FIG. 3A shows aschematic side cross sectional view of an edge ring 300 within whichmultiple probes 302 are embedded. FIG. 3B shows a schematic top crosssectional view of the edge ring 300 with eight probes 302, taken alongthe line IIIA-IIIB. For brevity, the probe circuit coupled to the probesvia conductor wire 304 is not shown in FIG. 3A.

As depicted in FIGS. 3A-3B, multiple probes or probe pins 302 arearranged circumferentially at a preset angular interval about thecentral axis of the edge ring 300. It is noted that any other suitablenumber of probes 302 may be embedded in the edge ring 300. In anotherexemplary embodiment, the probes 302 may be electrically connected toeach other via an optional connection wire 306, wherein the connectionwire 306 may be formed of electrically conducting material and embeddedin the edge ring 300. In this embodiment, all of the probes 302 may becoupled to the probe circuit.

The shape, dimension, and material compositions of the probe areselected according to the type of application thereof. In one exemplaryembodiment, the diagnostic sensor may include a plurality of thin platescoupled to a probe circuit, each plate having a generally polygonal orcircular plate/disk shape. For instance, FIG. 4A shows a schematic crosssectional view of an exemplary embodiment of an edge ring 400. Asdepicted, the multiple probes 402 are circumferentially arranged andembedded in the edge ring 400. Each probe 402 has a flat circular diskshape and coupled to a probe circuit (not shown in FIG. 4A) via aconductor wire 404. It is noted that the probe 402 may have othersuitable shapes, such as rectangular.

Optionally, the multiple probes 402 embedded in the edge ring 400 may beconnected to each other by a connection wire 406, wherein the connectionwire 406 may be formed of electrically conducting material and embeddedin the edge ring. In this embodiment, all of the probes may be coupledto the probe circuit via a conductor wire.

FIG. 4B shows a schematic cross sectional view of another embodiment ofan edge ring 410. As depicted, a probe 412 having an annular shape isembedded in the edge ring 410. For brevity, the probe circuit coupled tothe probe 412 via a conductor wire 404 is not shown in FIG. 4B.

The diagnostic sensors of FIGS. 1-4B can be applied to other suitablecomponents, such as confinement rings, that can be eroded by actions ofthe plasma and made of electrically insulating or dielectric material.Signals from multiple diagnostic sensors associated with thesecomponents can be simultaneously monitored to diagnose the conditions ofthe components in real time. For components made of conducting orsemiconductor material, such as the upper electrode 102 (FIG. 1), theprobe can be surrounded by dielectric material in order to prevent adirect contact between the probe and host component in which the probeis embedded, as discussed in conjunction with FIGS. 5-7B. Hereinafter,for the purpose of illustration, an upper electrode is described as anexemplary host component formed of conducting material.

FIG. 5 shows a schematic cross sectional diagram of an exemplaryembodiment of an upper electrode 500 that might be used in the plasmaprocessing chamber in FIG. 1. FIG. 6 shows a schematic cross sectionaldiagram of the upper electrode 500. For brevity, the detailedconfiguration of the electrode, such as gas injection mechanism, is notshown in FIGS. 5-6. As depicted, the upper electrode 500 is associatedwith a diagnostic sensor 501 that includes one or more probe units 503embedded in the upper electrode. Each probe unit 503 has a probe 502including a pin or wire segment formed of conducting material, such asmetal, and an insulating layer 504 surrounding the probe to electricallyinsulate the probe from the upper electrode 500. The insulating layer504 may be formed by, for example, a coating of dielectric material onthe probe 502. The sensor 501 also includes a sensor circuit 506 and oneor more conductor wires 508, each of the conductor wires 508 beingcoupled to the sensor circuit 506 and a corresponding one of the probes502. The conductor wires 508 can be electrically insulated from theupper electrode 500.

In one exemplary embodiment, each probe 502 can be individually coupledto the probe circuit 506 via a conductor wire 508. In another exemplaryembodiment, the probes 502 can be electrically connected to each otherby an optional connection wire 506, wherein the wire 506 is embedded inthe upper electrode 500 and insulated from the upper electrode by aninsulating layer, such as dielectric coating, surrounding the wire 506.In this embodiment, all of the probes 502 are coupled to the probecircuit 506. The probe circuit 506 may have components and operationalmechanisms similar to those of the circuit 118 in FIG. 1.

In yet another exemplary embodiment, each probe can include a thin platethat is formed of, but not limited to, conducting material and has agenerally round or polygonal shape. For instance, FIG. 7A shows aschematic cross sectional view of an exemplary embodiment of an upperelectrode 700, taken along a direction parallel to the line VI-VI (FIG.5). As depicted, each of the multiple probe units 703 embedded in theupper electrode 700 includes a probe 704 having a flat circular diskshape and an insulating layer 702 surrounding the probe to electricallyinsulate the probe from the upper electrode 700. It is noted that theprobe 704 may have other suitable shapes, such as rectangular. It isalso noted that any suitable number of probes may be used in the upperelectrode.

Optionally, the multiple probes 704 may be connected to each other by aconnection wire 706 that is similar to the connection wire 506 (FIG. 5).In this embodiment, all of the probes are coupled to the probe circuitvia a conductor wire.

In still another exemplary embodiment, the probe embedded in the upperelectrode may have a generally annular shape, as shown in FIG. 7B. FIG.7B shows a schematic cross sectional view of an upper electrode 710. Asdepicted, a probe unit 713 embedded in the upper electrode 710 includesan annular probe 714 and an insulating layer 712 surrounding the probe714 and electrically insulating the probe 714 from the upper electrode710. The probe 714 may be formed of a conducting material, such asmetal, and coupled to a probe circuit similar to the circuit 118 in FIG.1.

FIG. 7C shows a schematic top cross sectional view of another exemplaryembodiment of an upper electrode 720. As depicted, multiple probe units723 may be concentrically embedded in an upper electrode 720 and eachprobe unit 723 includes an annular probe 724 and an insulating layer 722surrounding the probe and electrically insulating the probe 724 from theupper electrode 720. In the case where the upper electrode 720 includesmultiple gas holes to have a showerhead configuration, the radialspacing between probe units can include gas outlets therein. Theinsulating layer 722 and probe 724 may be respectively formed ofmaterials similar to those of layer 712 and probe 714.

It is noted that the probes described in FIGS. 3A-7C can be biased to apositive dc potential, preferably of 10-15 volts, relative to theground. For instance, the positive terminal of the power supply in FIG.5 is connected to the resistor while the negative terminal of the powersupply is connected to the ground. For brevity, the probes positivelybiased with respect to the ground are not described in detail. However,it should be apparent that the operational and structural features ofthe sensor embodiments having negatively biased probes are similar tothose of the sensor embodiments having positively biased probes.

While the invention has been described in detail with reference tospecific embodiments thereof, it will be apparent to those skilled inthe art that various changes and modifications can be made, andequivalents employed, without departing from the scope of the appendedclaims.

1. A method of diagnosing status of a consumable part of a plasmareaction chamber, the consumable part including at least one conductiveelement embedded therein, comprising: coupling the conductive element toa power supply so that a bias potential relative to the ground isapplied to the conductive element; exposing the consumable part toplasma erosion until the conductive element draws a current from theplasma upon exposure of the conductive element to the plasma; measuringthe current; and evaluating a degree of erosion of the consumable partdue to the plasma based on the measured current.
 2. The method of claim1, wherein the step of measuring the current includes: interposing aresistor between the conductive element and power supply in series;measuring a voltage across the resistor; and determining the currentbased on the measured voltage.
 3. The method of claim 1, furthercomprising: triggering a notification when the current increases to apreset threshold level.
 4. The method of claim 1, wherein the consumablepart is formed of conducting material and the conducting element issurrounded by electrically insulating material such that the conductingelement is electrically insulated from the consumable part.
 5. Themethod of claim 1, wherein the consumable part is formed of dielectricmaterial.
 6. The method of claim 1, wherein the conducting element has apin shape.
 7. The method of claim 1, wherein the conducting element hasa generally polygonal shape.
 8. The method of claim 1, wherein theconducting element has a generally annular shape.
 9. The method of claim1, wherein the consumable part includes multiple conducting elementsthat are electrically connected to each other in series by a conductingwire.
 10. The method of claim 1, wherein the current is selected fromthe group consisting of positive ion current and negative electroncurrent.
 11. The method of claim 1, further comprising replacing theconsumable part with a new consumable part.
 12. A consumable part of aplasma reaction chamber, the consumable part including a surface to beexposed to plasma, comprising: one or more conductive elements embeddedin the consumable part; a probe circuit coupled to the conductiveelements; and a power supply coupled to the probe circuit and ground toapply a bias potential to the conductive elements relative to theground, wherein the conductive elements are operative to draw a currentfrom the plasma upon exposure of the conductive elements to the plasmaand the probe circuit is operative to measure the current.
 13. Theconsumable part of claim 12, wherein the consumable part is ofdielectric material and is selected from the group consisting of edgering and confinement ring.
 14. The consumable part of claim 12, whereinthe power supply is a DC power source.
 15. The consumable part of claim12, wherein the probe circuit includes a resistor and a voltmeter tomeasure an electrical potential across the resistor.
 16. The consumablepart of claim 12, wherein each of the conductive elements has a shapeselected from the group consisting of pin, polygonal, circular, andannular.
 17. The consumable part of claim 12, wherein the conductiveelements are electrically connected to each other by a conductive wire.18. The consumable part of claim 12, wherein the consumable part isformed of conductive material and the one or more conductive elementsare embedded in the consumable part and electrically insulated from theconsumable part by a dielectric layer.
 19. The consumable part of claim18, wherein the consumable part is an electrode for generating theplasma.
 20. A method of processing a semiconductor substrate in a plasmareaction chamber including the consumable part of claim 12.